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Nasa Picks "juno" As Next New Frontiers Mission
Guest_vjkane2000_*
post Jun 22 2005, 09:10 AM
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QUOTE (JRehling @ Jun 21 2005, 08:31 AM)
Indeed. Finding some impact craters is one of the ones that excites me more, because that would provide some sharp-shooting information regarding the cratering rate -- information that could be nigh impossible to find elsewhere in the jovian system.
  I'm still enamored of the orbit that makes use of two Io intercepts. If they were 180 degrees apart, then flybys could alternate in terms of geometry/lighting, and 50 "survived" perijoves would mean 25 looks at each hemisphere. Europa and Ganymede would cycle through 4 and 8 relative positions when the craft crossed their orbital radii, and that might mean regular flybys in fixed lighting conditions, if dumb luck wills it. If they were 120 degrees apart, then you could set the apojove so that the flybys would cycle through three relative Io positions: one third (~17) each with a flyby at two positions, and a third would have no Io flyby, but would likely enable some nice geometry for Europa/Ganymede (they would cycle through six and twelve positions -- it seems assured that at least four decent flybys of Ganymede, albeit in the same lighting condition, would take place).

  I am ignoring the fact that the Galileans can yank a craft's orbit around. Those nudges could either be utilized to willfully vary trajectory geometry or could alternately be overcome with a little propulsion...

  Indeed, if Europa Orbiter has a Galileo-2-ish midgame and an Io Observer had some of that worked into its primary mission, there'd be not much need for a dedicated-to-general-purpose Galilean/Jupiter craft in jovian orbit anytime soon. I suspect that, all things being equal, Io would end up trumping Ganymede/Callisto as a single priority, although the latter and larger pair would get the best coverage from any orbiter that was not specifically intended to be Io-devoted.
*


I would love a mission that does everything you say (alternating encounter points, etc), but I worry about the orbital mechanics. Either each flyby would have to use a gravity assist to tweak the timing of the next enounter, or fuel would have to be burned to do so. This would be complicated by the fact that at least some of the encounters would have to use gravity assists to walk the orbit so that the movement of Jupiter (taking Io with it) doesn't move the encounter point.

The alternative idea of using polar orbits has its own problems. Roughly 1/3 of the surface below the encounter point can be imaged well. If you come in at Io's poles, half of this area is in darkness (although you should be able to pick up 1/2 of the other pole on the way out). In theory, you could just pass by Io on the sunward side, say 10,000 km out, and see the poles and the sunlit side. Unfortuantely, you then lose the gravity assists that allow you to walk the orbit to counter Jupiter's movement around the sun. Not too long after you entered orbit, you'd be passing on the dark side of Io.

Anyone know enough about celestrial billards (ie, using gravity assists) to know if these problems can be reasonably handled?
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Guest_BruceMoomaw_*
post Jun 22 2005, 10:52 PM
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Well, keep in mind that Cassini's 45 close flybys of Titan over 4 years -- using only Titan itself to reset the shape of each orbit -- cover a really impressive variety of spots on its surface at closest approach. I see no reason why you couldn't do the same thing for a comparable number of Io flybys, especially since you would have four moons, rather than one, to modify the craft's orbit between flybys. (William Smythe's "Getting back to Io" paper does say that it's a lot easier to vary the longitudes of close approaches to Io than their latitudes; but Cassini does quite a lot of both during its Titan flybys.)

As John Rehling says, this mission (along with Europa Orbiter) would also make so many close flybys of Ganymede and Callisto that a mission devoted specifically to those two moons would very likely be superfluous (as, I think, a Jupiter Flyby with Muitple Entry Probes is also likely to be for quite a while, given the combination of the Galileo entry probe and Juno).
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Guest_BruceMoomaw_*
post Jun 29 2005, 06:02 PM
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The presentations from the June OPAG meeting are now online:

http://www.lpi.usra.edu/opag/jun_05_meeting/agenda.html

Perhaps the most interesting are the two on the new design of the Europa
Orbiter. This work is now very advanced and detailed, and the science
payload has been greatly enlarged from the earlier design -- although it
still seems questionable that a small lander could be added. (They may also
be aiming for a launch as early as 2012.)

http://www.lpi.usra.edu/opag/jun_05_meetin...E_Mission_Study.
pdf
http://www.lpi.usra.edu/opag/jun_05_meetin..._Science_Instru
ments_Trace_OPAG.pdf

However, most of the others are also of note. Note in particular the piece
about work on two possible Titan mission designs -- one of which consists
not of an aerobot, but of a small surface rover with inflatable wheels,
which might be able to drive 500 km in 3 years. (The other, oddly enough,
is simply a Titan orbiter -- no aerobot mission design is presented here,
although it's very unlikely that the concept has been rejected.)

http://www.lpi.usra.edu/opag/jun_05_meetin...s/opagtitan.pdf
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imran
post Jun 29 2005, 08:37 PM
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Thanks for the links, Bruce. I am surprised too that they are not considering an aerobot ("blimp") mission for Titan. The orbiter mission concept sounds like Cassini Huygens mission part two, with global coverage and a little more capability. The rover mission would also not do justice to a dynamic place like Titan.
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Guest_BruceMoomaw_*
post Jun 29 2005, 10:28 PM
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This hardly means that they're not considering a Titan aerobot -- it just means that one was not the subject of those particular two studies. I imagine that even the basic form of a Titan mission is still wide-open, and will remain so both until Cassini returns a lot more observations and until theorists have had a chance to chew over just what its data actually says about this complex and still very mysterious place.

The most encouraging thing to come out of those OPAG presentations is just how serious NASA finally seems to be -- at long last -- about flying a Europa mission.
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Guest_BruceMoomaw_*
post Jun 29 2005, 10:31 PM
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And, for one recent JPL study of a Titan aerobot mission, see one of the presentations from the preceding OPAG meeting in February:

http://www.lpi.usra.edu/opag/feb_05_meetin...resentation.pdf
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JRehling
post Jun 30 2005, 05:20 PM
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QUOTE (BruceMoomaw @ Jun 29 2005, 03:31 PM)
And, for one recent JPL study of a Titan aerobot mission, see one of the presentations from the preceding OPAG meeting in February:

http://www.lpi.usra.edu/opag/feb_05_meetin...resentation.pdf
*


It seems that the case for an aerobot is seriously helped by the fact that we have hardly a clue how drivable Titan's light-colored terrain might be, and the Huygens view makes it look like no wheeled craft would have a prayer. It would likely roll into a crevice, or land somewhere surrounded by crevices, and have its mobility quickly put to an end! It's possible that we could get useful recon from, eg, radar (Cassini's or Earthbound) and ascertain that there are smooth areas, but an aerobot easily trumps this possibility. I'd rather have a three-instrument aerobot floating over many kinds of terrain than a standout instrument package on wheels.

Ditto for Venus... Although I think a stationary lander would be sufficient for many purposes there. Big difference: we've already seen multiple landing sites on Venus, which surely represent most of the terrain of that whole world, vs. one on Titan, which surely doesn't!
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Guest_BruceMoomaw_*
post Jun 30 2005, 06:50 PM
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Actually, we DO need more surface observation points on Venus. One of the highest-priority goals of landings (specified in the new Roadmap) is to look for patches of granite or andesite crust which would indicate the existence of oceans on ancient Venus -- and the best place by far to look for those is in the "tessera" patches, which have been the top-priority landing sites for any American Venus mission for years. We would also like to take a look at those puzzling areas of high radar reflectivity on Venus' high-altitude terrain -- and, on top of that, keep in mind that even the Soviet landers didn't do any mineralogy at all of their own basaltic landing sites.

The question is whether the best way to do this is by a surface rover, an aerobot, or a larger number of multiple stationary landers. Frankly, I'm inclined to go with the latter -- we have the technology for those RIGHT NOW. (We might also be advised to try to develop in-situ age-dating instruments for Venus' surface; we have already done some promising initial work on those, and God knows it would be easier than a Venus sample return -- which I expect to see Congress fund on the same day O.J. finds the real killers.)
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tedstryk
post Jun 30 2005, 06:58 PM
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QUOTE (BruceMoomaw @ Jun 30 2005, 06:50 PM)
Actually, we DO need more surface observation points on Venus.  One of the highest-priority goals of landings (specified in the new Roadmap) is to look for patches of granite or andesite crust which would indicate the existence of oceans on ancient Venus -- and the best place by far to look for those is in the "tessera" patches, which have been the top-priority landing sites for any American Venus mission for years.  We would also like to take a look at those puzzling areas of high radar reflectivity on Venus' high-altitude terrain -- and, on top of that, keep in mind that even the Soviet landers didn't do any mineralogy at all of their own basaltic landing sites. 

The question is whether the best way to do this is by a surface rover, an aerobot, or a larger number of multiple stationary landers.  Frankly, I'm inclined to go with the latter -- we have the technology for those RIGHT NOW.  (We might also be advised to try to develop in-situ age-dating instruments for Venus' surface; we have already done some promising initial work on those, and God knows it would be easier than a Venus sample return -- which I expect to see Congress fund on the same day O.J. finds the real killers.)
*


It should also be noted that the Venera landings were far from random. Most cluster around the same region.


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JRehling
post Jun 30 2005, 07:15 PM
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QUOTE (BruceMoomaw @ Jun 30 2005, 11:50 AM)
Actually, we DO need more surface observation points on Venus.  One of the highest-priority goals of landings (specified in the new Roadmap) is to look for patches of granite or andesite crust which would indicate the existence of oceans on ancient Venus -- and the best place by far to look for those is in the "tessera" patches, which have been the top-priority landing sites for any American Venus mission for years.  We would also like to take a look at those puzzling areas of high radar reflectivity on Venus' high-altitude terrain -- and, on top of that, keep in mind that even the Soviet landers didn't do any mineralogy at all of their own basaltic landing sites.


All good points; I meant that we know what the terrain is like on representive locations on Venus, and we could say that a rover would operate with no problem on Venera 10/Venera 14 terrain, and not much problem on Venera 9/Venera 13 terrain. Of course, we can easily radar-survey Venus to find slopes and roughnesses at arbitrary scales.

The kinds of terrain you mention are indeed different and worth checking out. And may be tough to rover on, in the case of tessera; tough to hit precisely in the case of the radar-bright heights.

I'd aim for identification of granite from above rather than trying to hit the bullseye with a tessera lander. I don't know if the high temps + CO2 allow an IR spectroscopic approach from aloft below the clouds, but a TES (instrument on Mars
Global Surveyor) -type survey would give loads of coverage if flown on a balloon or airplane that cruised over one of the big tessera areas. I'd be afraid of committing too much money to a lander (even a rover) and landing in the wrong valley, one valley over from the geologically older one. Venus is a big place, and just as current Mars lander site selection depended upon orbital surveys to do us much good, we would be well served by some light/broad recon of Venus before we pay for landers.

QUOTE (BruceMoomaw @ Jun 30 2005, 11:50 AM)
The question is whether the best way to do this is by a surface rover, an aerobot, or a larger number of multiple stationary landers.  Frankly, I'm inclined to go with the latter -- we have the technology for those RIGHT NOW.  (We might also be advised to try to develop in-situ age-dating instruments for Venus' surface; we have already done some promising initial work on those, and God knows it would be easier than a Venus sample return -- which I expect to see Congress fund on the same day O.J. finds the real killers.)
*


We don't have the technology for long-duration Venus landers right now -- well, unless nuclear-powered refrigeration is the way we keep the instruments alive. An aerobot may or may not require less technological development than a seriously long-lasting Venus stationary lander, because the ability to go aloft into the cool heights is certainly more of a no-moving-parts approach than the refrigeration method. Whichever is easier, a stationary Venus lander with seismometry is a must-have at some point. But I disagree that a lander-first surely offers the best science/cost plan. Another entry in the field is also a very small, VAMP-like probe that aces the isotopic analysis of the atmosphere.

I might say that a good candidate for the next Venus mission would be an isotopic analyzer that also tested some multispactral imaging on a surface unit boundary to see what an aerobot/airplane could do with a longer below-cloud groundtrack.
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Guest_BruceMoomaw_*
post Jul 1 2005, 01:01 AM
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(1) "All good points; I meant that we know what the terrain is like on representive locations on Venus, and we could say that a rover would operate with no problem on Venera 10/Venera 14 terrain, and not much problem on Venera 9/Venera 13 terrain. Of course, we can easily radar-survey Venus to find slopes and roughnesses at arbitrary scales.

The kinds of terrain you mention are indeed different and worth checking out. And may be tough to rover on, in the case of tessera; tough to hit precisely in the case of the radar-bright heights."

Actually, the radar-bright heights are pretty big -- much of Venus between 2.6 and 6.6 km above the global mean (but not higher!) has this mysterious property, about which there are several theories. Perhaps the most plausible is that it's high-altitude "snow" -- made out of galena.

(2) "I'd aim for identification of granite from above rather than trying to hit the bullseye with a tessera lander. I don't know if the high temps + CO2 allow an IR spectroscopic approach from aloft below the clouds, but a TES (instrument on Mars Global Surveyor) -type survey would give loads of coverage if flown on a balloon or airplane that cruised over one of the big tessera areas. I'd be afraid of committing too much money to a lander (even a rover) and landing in the wrong valley, one valley over from the geologically older one. Venus is a big place, and just as current Mars lander site selection depended upon orbital surveys to do us much good, we would be well served by some light/broad recon of Venus before we pay for landers."

This returns me to the question of whether Venus' clouds and dense atmosphere actually allow us to do any mineralogy whatsoever from orbit -- a question about which there is still debate. I promised earlier to look this up for you, and will do as soon as I get a chance to stop juggling other plates. But there is a real chance that Venusian mineralogy is impossible from more than a small distance above the surface. (Very detailed SAR mapping -- and microwave or near-IR radiometry to look for volcanic hot spots -- are, on the other hand, entirely practical. A small -- quite possibly Discovery-class -- orbiter to do all that seems like a very good idea, and in fact was recommended by the DPS White Paper group advising the Solar System Decadal Survey a few years ago.)

I doubt that thermal-emission spectrometry is practical on Venus even at the surface -- there is far too much interference from its hot, extremely dense atmosphere. Indeed, even near-IR spectrometry of Venus' surface presents problems, because it's so hot that it actually glows dull red at night -- that is, its near-IR light from actual thermal emissions intermixes with that from its reflected sunlight in the daytime, scrambling their spectra up together. To sort out Venus' near-IR spectra (at longer than about 1 micron wavelength) in the daytime, you need a flashlamp to take comparative spectra with and without that additional reflected light -- but this is impossible to do beyond a short distance.

(3) "We don't have the technology for long-duration Venus landers right now -- well, unless nuclear-powered refrigeration is the way we keep the instruments alive. An aerobot may or may not require less technological development than a seriously long-lasting Venus stationary lander, because the ability to go aloft into the cool heights is certainly more of a no-moving-parts approach than the refrigeration method. Whichever is easier, a stationary Venus lander with seismometry is a must-have at some point."

A central part of the new Solar System Roadmap is a plan to develop solid-state electronics that CAN function at Venusian surface temperatures, so that we can fly a long-lived surface lander within the "Small Flagship" budget (less than $1.4 billion) around 2024. According to the Roadmap, we already have electronics that can function at up to 300 deg C -- but that's still not enough yet. However, there seem to be no automatic show-stoppers. As for nuclear-powered refrigeration, Mike Malin's 1992 proposal for a long-lived Venus seismic lander would have used 97% of its RTG's power just to keep its electronics cool!

And as for the aerobot: the trouble there is that we also have been unable to find a plastic so far suitable to make a balloon that can survive Venusian temperatures. NASA was counting on one called polybenzoxasole, which can do so -- but, according to http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1223.pdf , they have apparently been unable to find a way to make leakproof seams in it. Thus the proposal in that abstract for a two-stage balloon, with the surface stage consisting -- remarkably -- of a cylindrical, thin-walled stainless steel bellows inflated with helium, which need expand only to modest volume to lift the craft off in that dense atmosphere and loft it to the 370 deg C. level -- at which point a balloon which we know CAN survive that temperature can be released from an insulated container to loft the craft all the way back up into the clouds. The trouble is that you can only use this setup for one landing (and takeoff) at one point, since it will be extremely difficult to repack that second balloon into its insulated container again.

Now, when we do develop electronics capable of surviving Venusian surface temperatures, it will be possible to develop a rover which -- instead of rolling along the surface -- can actually inflate one of those small steel "bellows" balloons to lift just a few meters off the surface and cruise along like a research submersible along Earth's ocean bottom, using radar (or sonar!) to tweak the balloon's buoyancy and keep it at a stable altitude between touchdowns, and using Venus' slow surface winds and/or propellers to drive it horizontally. (This "balloon" would actually be more like a ballast tank.) I've actually mentioned this possibility to the Roadmap group, since they seem not to have thought of it.

Anyway, when you read the White Paper to the Roadmap Group written by the Venus Exploration Analysis Group ( http://www.lpi.usra.edu/vexag/venusexplorationrmap.pdf ), it turns out that they are thinking both of a rover AND a long-lived seismic network as possibilities for the 2024 Venus mission -- and they even suggest that the choice may depend on whether earlier missions show still-active volcanoes on Venus.

(4) "But I disagree that a lander-first surely offers the best science/cost plan. Another entry in the field is also a very small, VAMP-like probe that aces the isotopic analysis of the atmosphere."

I agree -- and so did the Decadal Survey White Paper group, who called such a Discovery-class entry probe (also to detect near-surface gases) the highest priority right now for Venus exploration. (Amazing how much we still don't know about Venus' atmosphere, given the number of probes that have been dropped into it.) Indeed, this goal -- which is currently incorporated into the goals of the proposed New Frontiers short-lived Venus lander, which has already had to be downscaled due to cost problems -- could very easily be split off to such a separate mission, making it possible to turn the NF mission into 2 or 3 short-lived landers that would focus entirely on the surface.

(5) "I might say that a good candidate for the next Venus mission would be an isotopic analyzer that also tested some multispectral imaging on a surface unit boundary to see what an aerobot/airplane could do with a longer below-cloud groundtrack."

This could indeed be easily added to such a mission (provided that you had the carrier bus fly by Venus during the drop to receive the photos at high speed). In this connection, note also the "VEVA" mission -- proposed twice for Discovery, but never a finalist -- which would use a balloon to both analyze atmospheric composition and drop four small impact probes equipped with cameras to image different types of Venusian terrain over several thousand km ( http://techreports.jpl.nasa.gov/1999/99-1959.pdf -- where it's called "VAMUS"). The problem, again, is getting good near-IR data on surface composition -- the VEVA probes would have multispectral cameras to try to get such data below 1 micron -- but the JPL paper I cite has an intriguing, vague reference to a possible souped-up version that would add a one-spot near-IR spectrometer and laser altimeter to each probe. Since a broadband laser has recently been developed, it's possible that the laser could also be used to illuminate the surface to let the descending VEVA probe get complete near-IR spectra of the surface. Once again, however, it might be wiser to split up VEVA's different functions among separate missions -- with one entry probe doing the VEVA balloon's mass spectral atmospheric analysis, and several full-fledged short-lived survivable landers that also take descent photos.

Needless to say, I think Doug had better move this discussion over to the Venus thread at this point.
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Guest_BruceMoomaw_*
post Jul 1 2005, 04:24 AM
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One more footnote here, which I forgot to include earlier, in response to John's comment: "I'd aim for identification of granite from above rather than trying to hit the bullseye with a tessera lander. I don't know if the high temps + CO2 allow an IR spectroscopic approach from aloft below the clouds, but a TES (instrument on Mars Global Surveyor) -type survey would give loads of coverage if flown on a balloon or airplane that cruised over one of the big tessera areas. I'd be afraid of committing too much money to a lander (even a rover) and landing in the wrong valley, one valley over from the geologically older one."

As with the high reflectivity regions -- but even more so -- it would be very hard to actually miss one of the tessera regions, which are often hundreds of km across. Also, it would be very good to be able to do some age-dating of a tessera patch (along with the main basalt plains, and maybe one of the more recent volcanic regions) in-situ with landers (although that experiment doesn't seem to have been on Larry Esposito's "SAGE" proposal for mutiple Venus landers for the last New Frontiers selection).

Once again, however, an excellent case can be made that -- before we dispatch any Venus landers at all -- we should fly another SAR mapping mission, with much higher resolution, in a low circular Venus orbit, as suggested by the DPS White Paper group a few years ago (and just repeated by the VEXAG group). As with Mars, a good deal of mapping reconnaissance is important in picking out the best possible Venusian landing sites, given the inevitable rarity of actual Venus landings.
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Guest_BruceMoomaw_*
post Jul 1 2005, 09:05 AM
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One small error on my part: the GCMS analysis of Venus' atmosphere on the proposed VEVA mission would have been done not by the balloon (which would only carry the four imaging drop probes, plus some weather sensors and a magnetometer) -- it would have been done by a completely separate large probe dropping all the way to the surface. Which, I don't think, changes any of my points at all. And now I'm switching all my future comments on this subject to the new "Future Venus Probes" thread that Phil Stooke has just opened up on this site. Time for us to get back to Jupiter here...
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john_s
post Jul 7 2005, 09:49 PM
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QUOTE (BruceMoomaw @ Jun 20 2005, 02:55 AM)
I need to talk with Spencer and Smythe as to whether this is the sort of orbit they might have in mind for the Observer.

*


I'm not sure what Bill Smythe had in mind, but I was definitely thinking of an orbit with perijove near Io and apojove out beyond Callisto somewhere, to minimize both delta-V and radiation exposure.

But right now, I'd be pretty happy if we could put a high-resolution camera on the revamped Europa orbiter and make high-frequency distant monitoring of Io (with ~1-km resolution) a priority for that mission in the months prior to Europa orbit insertion. You can do a lot with Io without close flybys, if you have the right instrumentation.

John Spencer
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Guest_BruceMoomaw_*
post Jul 8 2005, 02:07 AM
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Ah. Thankee for the information, John. As for that high-resolution camera, its inclusion on Europa Orbiter now seems almost certain:
http://www.lpi.usra.edu/opag/jun_05_meetin..._Trace_OPAG.pdf

The fact remains that we obviously still need lost more genuine closeup observations of Io as well.
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